The invention relates generally to improvements in television receivers. It is particularly directed to CCD (charge coupled device) comb filters for separating the luminance components from the color components of a television signal.
In NTSC type broadcast signals, luminance and color components are frequency-interleaved. At the receiver, those components are separated from each other and processed separately to develop a video image.
To effect the required separation between the luminance and color components, various well known types of filters may be employed. One such filter is known as a comb filter in which the combined video signal is processed along two parallel paths, one having an 1-H (one horizontal line interval) delay greater than the delay associated with the other path. The signals which are output from each path are combined so that color components are separated from luminance components. For good performance, the delay and gain associated with each path must be stable and accurate.
The delay paths for the comb filter are sometimes constructed of CCD devices, as described, for example, in U.S. Pat. No. 4,096,516. In the latter patent, three CCD delay devices are required to develop separated luminance and color signals. In addition, the video input to one of the delay devices must be inverted to obtain proper operation of the comb filter. The inclusion of the inverter makes it difficult to match the effective gain of all three delay paths, wherefore, gain adjustment is necessary. The need for such an adjustment is, of course, undesirable. Also, the need for three CCD delay devices renders the filter more complex than is desired.
In comb filtering systems of the type described above, it is customary to process the separated color signal to obtain relatively narrow band demodulated R-Y and B-Y color-difference signals. Although such narrow band signals are reasonably acceptable for use in developing a color image, it is understood in the television art that it is preferable to develop full bandwidth demodulated color signals, such as those commonly referred to as I and Q color signals. A system which employs fewer CCD delay devices to perform comb filtering, which eliminates the need for gain adjustment, and which provides wider band demodulated color signals would be particularly advantageous.